1. Technical Field
This technology pertains generally to ocular diagnostic imaging devices, and more particularly to a portable handheld smart phone-based retinal camera, capable of capturing high-quality, wide field fundus images. The use of the mobile phone platform creates a fully embedded system capable of acquisition, storage, and analysis of fundus images that can be directly transmitted from the phone via the wireless telecommunication system for remote evaluation.
2. Background Discussion
Since the late 19th century, when retinal imaging was first described, there has been steady technical improvement in imaging of the fundus of the eye. Digital fundus imaging is used extensively in the diagnosis, monitoring, and management of many retinal diseases. Access to fundus photography is often limited by patient morbidity, high equipment cost, and a shortage of trained personnel. Direct ophthalmoscopes, binocular indirect ophthalmoscopes, and funduscopic cameras are the standard of care for ocular examination and these devices can cost as much as $30,000 each.
One limitation found in current imaging systems is the bulky and stationary nature of the equipment. Standard fundus cameras are cumbersome tabletop devices that are not readily mobile due to the fragility, large size and heavy weight of these devices. Current tabletop fundus cameras also require the patient to be seated upright, which can be difficult for sick and hospitalized patients.
In addition to dimensional constraints, fundus cameras require a power source to supply power to the illumination, imaging screen, and data processing unit. Often this power source is provided by central in-wall power plugs, and continuous electrical power is required in order for the fundus camera to function properly.
An additional factor that increases the size and cost of current fundus imaging devices is the use of dedicated camera modules, dedicated computing systems, and dedicated storage systems for the capture, processing, and storage of the acquired fundus images.
Technical limitations also exist in fundus photography with current devices. Special consideration must be taken in order to obtain high quality images with limited reflections from the optical components of the system and the anatomical surfaces of the eye. Often, additional features and components are included in the optical system for the specific purpose of reducing system reflections. For example, some devices use a black dot lens to limit the reflection off of the lens in the system as well as the use of an apertured mirror to limit the reflection from the corneal surface.
The field of view of the retina is another technical specification of fundus imaging that is an important consideration in fundus camera development. Field of view describes the angle through the pupil at which the retina is imaged. The illuminating light from the device enters the retina and the reflected light from the retina is used to form an image on the sensor of the device. Many devices offer limited fields of view due to the increased complexity associated with wider fields. For example, typical direct ophthalmoscopes have a 5-degree field of view compared to a 45-degree field of view of standard fundus cameras.
Binocular indirect ophthalmoscopes produce an inverted image that is viewed by an ophthalmologist. Although ophthalmologists are trained to use this equipment, the use of a device that produces an inverted image is often difficult to use by the untrained user since it is not intuitive.
Finally, current standard bench top fundus cameras require the use of a dedicated computing system (i.e. computer, laptop, or any other secondary device) to receive and process the images.
Accordingly, there is a need for a low cost handheld device that can function as a substitute for these high cost medical devices, enabling the recording of digital images of the ophthalmic exam by both experts and non-experts that is also capable of transmitting these images for expert evaluation.